1. Field of the Invention
The present invention relates generally to brazed assemblies and, more specifically, to a method of making a braze sheet for a brazed assembly such as a heat exchanger.
2. Description of the Related Art
It is known to provide brazed assemblies such as heat exchangers. These heat exchangers may be condensers, evaporators, heater cores and coolers. Typically, the heat exchangers have alternating rows of tubes or plates with convoluted fins made of a metal material such as aluminum or an aluminum alloy. Many of these heat exchangers require external or internal brazing or a combination of both. Previously, the heat exchangers have been brazed in a vacuum furnace. Recently, a process known as "controlled atmosphere brazing" (CAB) has been used with non-corrosive fluxes. CAB brazing has been preferred over vacuum furnace brazing due to improved production yields, lower furnace maintenance requirements and greater braze process robustness.
It is also known that CAB brazing currently used to manufacture aluminum heat exchangers requires the use of fluxing agents being fluoride based in composition. The use of these fluxing agents with conventional aluminum heat exchangers promotes the dissociation and disruption of the native aluminum oxide (Al.sub.2 O.sub.3)and suppresses the formation of magnesium oxide (MgO)on the surface of the aluminum heat exchanger to promote wetting of the molten clad layer between mating components. Flux application is accomplished by applying the flux to preassembled heat exchanger components by suspending the flux in a carrier, typically water or alcohol with or without a binder, applying the flux to the exterior of the heat exchanger and thoroughly drying the heat exchanger to remove excess carrier which would inhibit brazing.
Although CAB brazing has worked well, it suffers from the disadvantage that the components of the heat exchanger require individual fluxing before assembly and an overall fluxing of the completed assembly before brazing. Also, CAB brazing suffers from the disadvantage that the fluxing of the heat exchanger is costly, time consuming and requires considerable floor space and processing time.